The present invention relates to the sterilization and disinfection arts. It finds particular application in conjunction with the evaluation of peracetic acid sterilization or disinfection baths and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable to other liquid sterilization and disinfection processes where the sterilant or disinfectant is effective above a minimum effective concentration, such as liquid hydrogen peroxide or sodium hypochlorite sterilization or disinfection systems.
Peracetic acid is a useful disinfectant and sterilant for a variety of applications including disinfection of waste and sterilization of medical equipment, packaging containers, and the like. Peracetic acid has the ability to be reused over a period of time, allowing instruments to be repeatedly sterilized or disinfected throughout the day in the same bath.
In use, peracetic precursors are mixed with water and other chemicals in a bath and the items to be sterilized or disinfected are immersed in the bath. Decontaminated items are then typically rinsed before use. To ensure effective sterilization or disinfection within a preselected period of time, the concentration of the peracetic acid is maintained above a minimum effective level, typically around 2300 parts per million for sterilization of medical instruments. For disinfection, peracetic acid concentrations of 5 ppm and above are used. For peracetic acid concentrations of at or above the minimum effective level, complete sterilization or disinfection is expected. Because the peracetic acid tends to decompose over time, it is important to evaluate the bath periodically to determine whether the minimum effective level of peracetic acid is present.
Currently, it is often assumed that the bath will be at or above the minimum effective concentration for a period of around eight hours where a selected initial concentration of peracetic acid is present in the bath. However, differences in ambient temperature, the quantity of items to be disinfected or sterilized and the level of contamination on the items can lead to considerable variation in the useful life of the bath. In addition, storage conditions sometimes lead to degradation of peracetic acid precursors before use. For medical instruments in particular, therefore, a more accurate method of evaluating the peracetic acid is required. Dippable chemically-treated papers are easy to use but lack accuracy, particularly at concentrations suitable for sterilizing and disinfecting. Although chemical titration methods provide an accurate measure of the concentration of peracetic acid in a solution, these methods are time-consuming and open to possible operator errors. Premeasured vials of titrating solution have been utilized to detect low and trace concentrations of peracetic acid, e.g., residual peracetic acid after sterilizing and rinsing. Manually measuring a unit volume of solution into the vial raises the specter of human error.
The present invention provides a new and improved wet chemical indicator for the evaluation of peracetic acid solutions which overcomes the above-referenced problems and others.